1. Field of Invention
The invention relates to methods and systems that compensate for polarization mode dispersion.
2. Description of Related Art
As data rates transmitted over optical fibers increase, the effects of polarization mode dispersion (PMD) become increasingly important. Polarization mode dispersion is a form of signal distortion and can be caused by subtle physical defects in an optical fiber giving rise to birefringence. A birefringent optical fiber conducting a modulated optical signal can temporally disperse the resulting optical frequencies of the optical signal. Furthermore, as environmental variables such as temperature fluctuate over time, the birefringent character of the optical fiber can change, thus changing the dispersion profile of the optical signal. Accordingly, there is a need for new technology to provide better PMD compensation.
The invention provides methods and systems for PMD compensation for optical communication systems having an optical transmitter, an optical receiver and one or more optical compensators.
As multiple optical signals having different optical frequency bands are transmitted by the transmitter, the optical compensators adjustably alter, or rotate, the polarization states of the optical signals as they traverse the optical compensators. The rotated optical signals are then received by the optical receiver, which can measure error conditions such as bit-error rates of the various optical signals.
If a particular optical signal exhibits an unacceptable error condition, the optical receiver issues commands to the optical compensators to change the polarization rotation angles of the various optical signals traversing the optical compensators. As the optical compensators change the polarization states, the PMD of each optical signal observed at the optical receiver can vary until all optical signals received by the optical receiver display acceptable performance.
Other features and advantage of the present invention are described below are apparent from the accompanying drawings and from the detailed description which follows.